1.C.13 The Channel-forming Leukocidin Cytotoxin (Ctx) Family

A single protein, Ctx of phage φCTX of Pseudomonas aeruginosa comprises the Ctx family. The cytotoxin is believed to form hydrophilic pores in target cell membranes. The inactive, cell associated (non-secreted) precursor is converted to the active toxin by protease digestion at the same time that P. aeruginosa lyses. Leukocidin (cytotoxin) is active against most eukaryotic cells, especially leukocytes. It exhibits a short region similar to corresponding regions in α-toxin from Staphylococcus aureus and aerolysin from Aeromonas species (residues 222-251). The soluble secreted protein inserts into the target cell membrane and probably forms a pentameric pore-forming structure.

The generalized transport reaction is:

Ions (in) ions (out)

This family belongs to the Aerolysin Superfamily.



Hayashi, T., Y. Kamio, and Y. Terawaki. (1989). Purification and characterization of cytotoxin from the crude extract of Pseudomonas aeruginosa. Microbial Pathogenesis 6: 103-112.

Hayashi, T., Y. Kamio, F. Hishinuma, Y. Usami, K. Titani, and Y. Terawaki. (1989). Pseudomonas aeruginosa cytotoxin: the nucleotide sequence of the gene and the mechanism of activation of the protoxin. Mol. Microbiol. 3: 861-868.

Nakayama, K., S. Kanaya, M. Ohnishi, Y. Terawaki, and T. Hayashi. (1999). The complete nucleotide sequence of φCTX, a cytotoxin-converting phage of Pseudomonas aeruginosa: implications for phage evolution and horizontal gene transfer via bacteriophages. Mol. Microbiol. 31: 399-419.

Sliwinski-Korell, A., H. Engelhardt, M. Kampka, and F. Lutz. (1999). Oligomerization and structural changes of the pore-forming Pseudomonas aeruginosa cytotoxin. Eur. J. Biochem. 265: 221-230.


TC#NameOrganismal TypeExample
1.C.13.1.1Channel-forming leucocidin cytotoxin, CTX Gram-negative bacteria

CTX of phage φCTX of Pseudomonas aeruginosa


Uncharacterized protein of 285 aas


UP of Pectobactyerium wasabiae


Cytotoxic Leucocidin of 290 aas


Cytotoxic leucocidin of Fibrella aestuarina


Uncharacterized protein with similarity to clostridial epsilon toxin ETX and Bacillus mosquitocidal toxin MTX2.


UP of Virbio caribbenthicus


Arthropod secreted salivary gland protein of 278 aas


Secreted protein of Ixodes scapularis


Secreted salivary gland protein of 291 aas.


Secreted protein of Oxytricha trifallax